12.3 Radiation Dose Calculations
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12.3 Radiation Dose Calculations
When preparing work on radiometric measuring systems, it is im-
portant to calculate the radiation exposure to be expected in ad-
vance, for this has consequences on the required safety precau-
tions.
The expected radiation exposure can be calculated quite easily and
with sufficient accuracy, provided you know the isotope and the
activity of the source used. You can take this information from the
source documentation or from the type label on the shielding.
The radiation exposure to be expected for a shielded source is cal-
culated as follows:
s
t k A
= D Dose
2
⋅
⋅⋅
A is the activity of the source and k the respective specific Gamma
radiation constant (see the table below). The distance from the
measuring point to the source is r and the duration of stay at this
point is t. s is the shielding factor of the shielding used; it is listed
in the shielding brochure or can be calculated. s = 1 when calculat-
ing the dose rate for work with an unshielded source.
NUCLIDE
k DIMENSIONS
Co-60 0.35
Cs-137 0.09
Sv * m
h * MBq
µ
2
Calculation example
The dose in a distance of 50 cm of a Co-60 source with an activity
of 350 MBq and a time of 30 minutes in this distance has to be cal-
culated. The source is shielded by a shielding with a shielding fac-
tor of 30:
Sv 8.2
=
30 MBq ) 5.0(
5.0 35.0 350
2
2
⋅⋅⋅
⋅⋅⋅
=
hm
hmSvMBq
D
µ
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